Manufacture of azo compounds



Patented Aug. 9, 1949 MANUFACTURE OF AZO COMPOUNDS Roy 0. Locke, Salem,N. J., assignorlto E. 1. du Pont de Nemours & Company, .Wilmington,Del., a corporation of Delaware No Drawing. Application October 1, 1945,Serial No. 620,396

This invention relates to the manufactureof azo compounds which findextensive use as pigmenting agents, and especially to novel processesfor converting certain of the azo intermediates into finished products,which are devoid of solubilizing substituents in a single reactionmedium.

Heretofore, it was customarily the practice in making azo compounds todiazotize the primary amine in an acid medium at a low temperature, say40 F., and then to mix this cold acid diazo solution, which has a low pHvalue of about 2.0, with an alkaline solution .of the couplingcomponent, which has a high pH value of about 10.7. In effecting thesecouplings in large or commercial lots much diificulty has beenencountered in controlling the methods used. Among these difiiculties isthe necessity of using relatively large excesses of diazo components anddiazotizing agents because of the relative instability of nitrous acidand the diazo of the primary arylamine in the diazotizing medium. Inacid, aqueous media of the concentration used for diazotization, nitrousacid reacts slowly with primary arylamines which are sparingly soluble,and the diazotization, as practiced heretofore, is consequently timeconsuming. Special treatments and highly skilled handling were necessaryin order to avoid the formation of decomposition products or by-productswhich have deleterious effects on the final products. Thecombining oftwo solutions of such widely differing pH value made necessary the useof coupling media having a varying pH value which traversed a wide pHrange during the mixing of the acid and alkaline solutions, and thiscondition favored the formation of products of inferior quality.Accordingly, the reactants were subjected to a wide range of conditionsduring the process of coupling wherein ample opportunity to form avariety of kinds and amounts of inferior coupling products ordisadvantageous by-products was afforded.

The production of by-products and inferior coupling products wasenhanced by these variables. The timing of different operators, or

even the timing of the same operators in manufacturing different batchesof products affected the products. Rates of combining the solutions,temperature variations, and volume relationships often became socritical as to be hardly capable of repetition in manufacturingoperations. It followed that pigments having wide variations inproperties and undesirable defects were pro- .duced sometimes inmanufacturing, operations from raw materials of the best quality andreme- 3 Claims. (01. 260-144) dial measures were wanting. Undesirednitrosa- 55 tion products were often unavoidably formed and theseimpaired the properties and yield of the coupled products. Constant orexact standards of manufacture were most diflicult to attain by theprocesses of the prior art and improved processes were desirable.

I have now discovered that many of the defects of the prior artprocesses can be avoided by the processes .of the present invention inwhich diazotization and coupling reactions are carried on in one and thesame reaction medium. The coupling reaction goes on at such a rapid ratethat it may be considered in effect to be simultaneous with or progresswith equal speed as the diazotization. In the processes of the presentinvention higher pH values are preferred than those heretoforeconsidered to be practicable for the diazotization of the diazocomponent and the coupling proceeds at the same pH. The bestdiazotization and coupling emciencies are attained by using completesolutions of the components. The range of pH value within which thedouble reaction of diazotization and coupling takes placeinstantaneously in the medium has been determined.

It is among the .objects of the present invention to provide novelimproved processes for manufacturing azo compounds which are devoid ofsolubilizing groups. Another object .of the invention is to provide asimplification of the diazotization and coupling reactions involved inthe manufacture of such compounds. A further object is to providemethods wherein diazotization and coupling take place instantaneouslyand in the same medium. Another object of the prescontaining thediazotizable component and an I alkaline water solution containing thecoupling component and a diazotizing agent, the mixing together of thesesolutions being at a rate and in such volume and concentrations that thepH of the resulting reaction mixture will be maintained at a pH value ofabout 6.0 to about 7.2 from the (a beginning of the mixing to the end ofthe reaction. It has also been found that the molar ratio of mineralacid to diazotizable amine should be about 2 to about 2.4 parts ofmineral acid to '1 part diazotizable amine and the temperature of thereaction medium should be at least about 70 F.

in order to attain the improved results. The mixture is desirably madeby continuously combining relatively small portions .of the solutions inunit time with continuous thorough mixing so as to avoid more than amomentary period of nonadjusted pH, the same being a short initialmixing perio'd'wherein'no considerable-couplin has taken place. This maybe done by slowlydrawing streams of both of the solutions from theirrespective containers and uniting the streams ima third container whilstmaintaining thepI-Lyalue of the mixture within the above stated rangeand maintaining thorough agitation of :thermixture. The compositions ofthe several-solutionszand the rate of withdrawal of solution fromeachyessel are regulated, by any convenient meanshsoeas to combine theacid, alkali and dye components'ln the above described desiredproportions. In general, about equimolecular proportions of'thecomponents of the azo compound are desirable, but :departure 1 therefromis :tolerable.

:The invention will .be .more -Iful1 .set?forth:in whet-following moredetailed descri-ption-.whichin eludes. examples that are'given asillustrativaem- 'bodiments of the. invention and. not-as limitationsthereof. Parts are expressed.inparts by weight mnlesscotherwisespecified.

Emamplej :A solution of diazotizable; primary: ar-yl mine .was :made by.adding 152 parts ;of ;para:-:nitroeortho-toluidine 100% (1 -mole) to500 .parts--o-i" (water with good agitation and-stirring until :25,quniiorm slurry was obtained, then 7730 parts-of hydrochloric acid (2-;n1oleseHGl-w100%) .were added with stirring until jaluniformrsuspen--;sion was obtained. The liliXtLllB;W&S diluted --to {7000. parts :withwater at 70 Fnandgstirreds minutes to obtain a complete solution-ofthe-in .tcrrnediate. It was then madeuptoafinal-vel .ume,of'15,000 partsby addingiwat-er at ,-7-5 F. .The .final 1 temperature was adjusted. to100 ,A solution of coupling component was madepby mixing together 262parts of thelanilide of beta- .l ydroxy-naphthoicacid.100% 1.-mo1e),0400 parts .caustic soda. 10% .(1 mole--NaQH-..100-%) {and 210parts Turkey red, oil 50% (5;partsisu1f0nated .castoroil 100%) andheating .to.160,Fmwitlngood agitation, then :adding .2000 partsof waterrand holding the; temperature 'at 160 untilithe. intermediate was:completely dissolved. isi'xtyr 'iinc .partsof sodium nitrite (1 mole:100% were a'ddzedtwith stirring until completelycdissolved. :jIfhe.solutionwas then 1111346191111 ozwatfinalivolume .nf .15,00,0 partswith water and theztemnerature wa adjustedato 150 F.

T-IIheISQIUtiDHLOfI dia-zo :componentmnd .the: solution :-of couplingcomponent .WEI'GI'CmIXBd 21in :a third reaction vessel by pourinthemzintmthe vessel atnai regular rate during a: fioeminute -period land:ccntrolling the rates :to maintain a :pH in the :mixture :ranging: from6.0 ito 2722 throughout atheipombiningoperation. The usual tests IfOIcompletenessof :coupling and finakpI-I: were-made thereafter.

The pigment thus. formed-waszfilteredzroutand washedwith waterzatu75 F.iThezfilterlca-ke" was dried at1140 .;F.;and :the dry.pigment-.wasground tDf'iEfl'fiflBf powder. 5A bright'red pigment :was:obvtamed:iny-ields of 99;8% of theory.

When-tested-as a lithographicfihkthe masstone :Was darker and nrthe-.tinctoria1 .xstreneth .;l53% greater rthan .12. "product made by athewpriorqart method v:of .rpreforming 1 thexdiazo and zthcnccupling it tothe second component in separate media.

Instead of using the batch process described above, the solutions may bemetered into a small vessel fitted with a high speed agitator. Thepigment slurry can then be drawn oif continu- .ou$i rbyi;overfiow,dewatere'd=;arrd dried by com -tinuous methods commonly employed "forsuch purposes. .10

Example II Apaste-composed of 212.6 partsof 313 ,dichlor -ben,zidine100%'(015 mole) in 7876 parts 310% h drochloric aci'd'( 2;4.mo1es"HCl"1'00%).was ajdd- Ed'tofI-OGO partsof wate1'. at"75iEandheatedto =I'80"'F. 1Then'5000 parts water.. at ".1180I1?. ,wereajci'c 1ed --and the mixture was stirred ,until ,com- "plete solution ofthe intermediate .Was-Abteinen. The; resulting solution was treatedwithj25. parts -of" Fiitercel--and 175 parts of iNuehar;.stirne;d lfiminutes, filtered and made up to'1;0;000 pants with "Water to ;obtain aclear solution' at,;180IF.

"Agpaste composed of 178 partsacfitqacetaniiide 100% (1mole) in;5000parts ,water atf'Z511*f. was

* added-to'960partsof 10% causticsodacgemoies 'Na'DH 100%) and stirredat"'75 until ,complete-solution-iwas obtained. Then 69 part pf sodiumnitrite '-100% (1 mole) and ifi partsjior- -mic acid 100% '(1 mole) werea'ddedjinturnand the solution was; made up to 102 0 pants .with

water-at F.

"The-first of the above solutions atj IL and the-secondsolutlon at-75"F. .weregrajdufllyand simultaneously added to 15,000 partspf water at59 F. *du-ring1a130 minute period whilstmaintaining a temperature 3 ofION-3120975. a r;d a,p1-I :QI "6 15-7-32 -throughout the combiningoperation. The'usual tests for completeness ofcoupling and finalpH-were'made and, the mixture .Wsfitiirfid 55 fer'-2 hours,,a.t thistemperature and'fina'llyheatezi to-190 Fpfor 30 minutes.

Thgresulting product of coupling wa jiiltereld ofiwthe press cake was"dried at 1?. ;an1l"'the dry-color wag-pulverized.

"I'he ellow pigment was obtained inapproximately-theoretical yield. Itgave ajfiithographic ink' -havinga dark: masstone and a reddeigshadethan theinkifrom -pi gment madefrqm the. same intermediates bycouplinga; preformed, tetraz o' to 65 the second component. The "pigmentis more stable-than pigments made from the-same -components'by-priorartprocesses.

Example. I V

A 'contin-uous process for makingazo pigment "dyestuffs may be carriedout by preparin solutions as descr-ibe'd in Example I, metering thesesolutions severally into the suction side or? a pump in tthe:proportions :that 1 they :are mixed r in ac- 75 cordarxee awith rtheprocedure of 'Exa-mple '+'I i-ior rapidly mixing them. The solutions arethen passed into a coiled tube which may be baflled on the inside formore vigorous agitation, or through a small diameter tube at such a ratethat turbulent flow is produced, such as that described in United StatesPatent No. 2,021,143 to Calcott and Williams. Heat may be applied to allor part of the coil if desired. The finished pigment slurry which comesfrom the end of the coiled tube can then be dewatered, washed and driedcontinuously by standard mechanical methods.

The concentrations of the several solutions which are mixed to form thereaction mixture may be varied over a wide range but the content ofsolids in the initial solutions should not exceed that which iscompletely in solution. Care should be taken to mak the mixture so thatall diazotization takes place in a medium having a pH value betweenabout 6.0 and about 7.2. The ensuing coupling thereupon immediatelytakes place in a medium having the same pH range rather than in onehaving the wide change in pH from about 10.7 to about 6.5 to 7.0 whichis produced, for example, by adding gradually an acid solution such asthat described in the examples to an alkaline solution. In such agradual mixing of the acid component into a mass of coupling componentin alkaline solution, a condition commonly encountered in commercialmanufacturing operations, the reaction at the start would take place ina medium having a pH value of about 10.7 and this value would begradually reduced to a pH value of 6.5 to 7.0 at the end. However, whenthe mixing will have been completed in such manner a large proportion ofthe coupling or other reaction will have been completed in a high pHmedium and the products will have the undesirable properties of productscoupled in high pH media, among which is the varying crystallinestructure and intermediate products which are not produced in theprocesses of the present invention.

In the present process no energy is lost in cooling the solutions to lowtemperatures such as those approximating freezing and then heating themto room temperature or higher before the reaction is completed. In thepresent process, about room temperature, say, about 70 F., to as high asthe boiling point of the coupling medium give the best products, andthis temperature range is otherwise preferred for economic reasons.Large excesses of acid or alkali are not required in the processes ofthe invention. They may be used in stoichiometrlc proportions forproducing the final pH values herein pointed out. In all cases thealkali metal nitrite should be dissolved in the alkaline solution andthe primary arylamine should be dissolved in a non-oxidizing mineralacid. Since the nitrous acid is formed continuously as the mixture ismade, and it is used up as fast as it is formed, it is unnecessary toemploy excesses of alkali metal nitrite such as those which arenecessary in processes where the diazo is first made in a batch and thenmixed with the alkaline solution of coupling component. Theconcentrations of the components in the water solutions can be variedover a wide range but it is necessary to employ complete solutions.

In the present process all the necessary ingredients and optimumconditions for diazotization and coupling are produced at one and thesame moment with the result that insoluble or partially solubleIcy-products are not formed. By producing these optimum conditionssimultaneously and without being accompanied with undesirable sidereactions, the pigment is formed in a desirable state of subdivisionwhich improves the properties of the product over products made inaccordance with prior art methods.

The present processes are susceptible of easy and accurate control andmore uniform products can be made than those which are produced by priorart methods. The present invention makes possible for the first time acontinuous process for the production of azo pigments. The inventionprovides processes whereb pigments of greater tinctorial strength anduniformity of shade are produced as compared to those produced by priorart processes.

I claim:

1. The process which comprises gradually mixing in small increments abody of mineral acid water solution of a diazo component which is devoidof water solubilizing acid groups and a body of an alkaline watersolution containing a diazotizing agent and a, coupling component whichis devoid of Water solubilizing acid groups, completely mixing thesolutions as fast as diazotization of the diazotizing agentprogressively takes place, and maintaining a mixture having a pH valueof about 6.0 to about 7.2, in the mixture, the acid and the diazotizableamino compound being present in about the proportion of 2 to 2.4 partsof mineral acid to 1 part of diazotizable amino compound, and thetemperature of the solutions being sufilcient to make a mixture having atemperature of about F. to the boiling point of the mixture. 7

2. A process in accordance with claim 1 in which the diazo component isnot in excess of that which will couple with all of the couplingcomponent present in the mixture.

3. A process in accordance with claim 1 in which the acid and thealkaline solutions are continuously and gradually mixed in a receptacle,and the resulting slurry containing the coupled product is continuouslyremoved from the receptacle.

ROY C. LOCKE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,922,463 Turskl Aug. 15, 19331,999,026 Tramm Apr. 23, 1935 2,025,916 Tramm Dec. 31, 1935 2,182,721Conzetti Dec. 5, 1939 2,277,778 Randall Mar. 31, 1942 2,349,561 ReynoldsMay 23, 1944 2,410,219 Langstroth Oct. 29, 1946 OTHER REFERENCESSaunders, The Aromatic Diazo-Compounds and their TechnicalApplications," London, 1936, pages 4. 5, 9, 104, 118.

